A figure from ancient folklore, the doppelganger--in fiction a character's sinister look-alike--continues to appear in literature, television and film. The modern-day version (of the Doppelganger, or "double-goer" in German) is typically depicted in a form adapted to reflect present-day social anxieties. Focusing on a broad range of narratives, the author explores 21st century representations in novels (such as Audrey Niffenegger's Her...